by **Benn Roe** » Wed Nov 28, 2018 10:47 am

If you're runnng the cabs in series like that (one into the other, rather than both directly from outputs on the amp), all you have to do is add up the impedance of the individual cabs to get their total. The number you set the head for is the amp's minimum impedance, so make sure you set the amp to the highest number you can that is lower than or equal to the impedance of the cabs. The closer to the number, the better, but definitely don't let the speakers have lower impedance than what you have the amp set for.

In series, it sounds like the lowest you could get your speakers to would be 12 ohms. You could safely connect the V2 set at 8 ohms (or any setting, actually), but it's been my experience that the the greater the disparity between the amp's minimum impedance and the speakers' actual impedance, the less power you get out of the amp. It just feels less efficient or something. Mind you, I don't know shit about electronics, I just forced myself to know speaker connection math so I wouldn't blow anything up; I can only relay the math, not explain why it works that way.

Since your amps each have two speaker outputs, you also have the option of running the cabs in parallel, which has drastically different math. If cab 1's impedance is A, cab 2's impedance is B, and the total impedance is C, the forumla is (1/A)+(1/B)=(1/C). So, Sunn at 8 and Sound City at 4 would give you a total impedance of 2.666666 ohms, which is pretty close to the 2 ohm minimum of both amps. Two cabs at 4 ohms each would be exactly 2 ohms. For what it's worth, I've had several amp techs warn me against trusting any minimum rating of 2 ohms, because it's too close to 0, but lots of amps from the 70s claim to be able to go that low, so who knows? The main difficulty is that amps almost always have minimums of 2, 4, 8, or 16, and I don't think there's a way to hit any of those numbers on the nose with your mismatched speakers. You'd need two 4 ohm, or two 8 ohm, cabs to get the math to work out perfectly.

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